I doubt it is Plum Sauce as it is rarely served in Thailand or Thai rerstaurants, but Hoisin mixed with chiles and chopped peanuts is often used as a dipping sauce. If you can't find Hoisin in your local Asian or regular market you can make it: Hoisin recipe: Ingredients: 4 Tablespoons Soy sauce - dark/light/usual 2 tablespoons Peanut butter - or black bean paste 1 tablespoon Honey - or molasses 2 teaspoons white vinegar 1/8 teaspoon garlic powder 2 teaspoons sesame seed oil 20 drops Chinese-style hot sauce 1/8 teaspoon black pepper Directions: Simply mix all ingredients by hand. At first it does not appear like it will mix, but keep at it just a bit longer and you have Hoisin Sauce. Letting it rest does not appear to improve the flavour any.